What is puberty?
Puberty is a time in your life that brings lots of growth and change…both on the outside and inside. It's the process of changing from a kid into an adult, even though you won't be all the way grown-up when it's over.

Basically, it's a time when your body becomes sexually mature -- that's medical-speak for your reproductive system starting to work, preparing you for the day, many years in the future, when you might decide to have children of your own.

By the time puberty's over, your body will be bigger and more "adult looking," and there will be more noticeable differences between you and someone of the opposite sex.

What causes puberty?
Hormones cause puberty. These are chemicals produced by your glands that tell the different parts of your body to change and mature. If you're baking a loaf of bread, you add yeast to the dough, right? The yeast is a special ingredient that makes the dough rise. Without it, the bread would be flat. Hormones are kind of the same thing. Your glands add them to your body -- like a special ingredient -- so you can grow up.

In girls, puberty is controlled by the hormones estrogen and progesterone.

In boys, puberty is controlled by a hormone called testosterone.

When does it happen?
Puberty doesn't begin on a specific date, like your tenth birthday (but wouldn't it be easier if it did?). It's different for everyone, but most kids will start noticing changes somewhere between 9 and 15.

This means that in sixth grade, a student sitting at one desk could be well into puberty, while the person at the next desk could be two years away from starting! As you probably know, this can cause all sorts of weird feelings and awkwardness, especially among friends who've always been at the same level of maturity.

The important thing to remember is that it's not a race. There's no shame in being the last in your class to hit the Big P, and there's no shame in being first. Puberty happens when it happens, and every person is on his or her own schedule. The important thing is to understand what's going on so that it doesn't take you by surprise or confuse you.

Did you know that puberty also has different schedules for girls and boys? Girls usually start puberty when they're 8 to 13 years old, while boys tend to start when they're 10 to 15 years old. This is why people often say that girls "mature faster," or accuse tween boys of being "so immature." It's also why some girls you know may stand several inches taller than their guy friends!

How long does puberty last?
Again, it's different for each person. Some girls and guys develop quickly, taking just two or three years to go through most of puberty's changes. For other kids, the various stages of puberty will take longer, perhaps four or five years. The important thing to remember is that puberty doesn't happen all at once. It's a slow, gradual thing, and includes a lot of changes.